package org.apache.lucene.analysis;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

/**
 * This class can be used if the Tokens of a TokenStream are intended to be
 * consumed more than once. It caches all Tokens locally in a List.
 * 
 * CachingTokenFilter implements the optional method {@link TokenStream#reset()},
 * which repositions the stream to the first Token.
 * 
 */
public class CachingTokenFilter extends TokenFilter {
	private List cache;
	private Iterator iterator;

	public CachingTokenFilter(TokenStream input) {
		super(input);
	}

	public Token next() throws IOException {
		if (cache == null) {
			// fill cache lazily
			cache = new LinkedList();
			fillCache();
			iterator = cache.iterator();
		}

		if (!iterator.hasNext()) {
			// the cache is exhausted, return null
			return null;
		}

		return (Token) iterator.next();
	}

	public void reset() throws IOException {
		if (cache != null) {
			iterator = cache.iterator();
		}
	}

	private void fillCache() throws IOException {
		Token token;
		while ((token = input.next()) != null) {
			cache.add(token);
		}
	}

}
